Acute Renal Failure Flashcards
How is Acute Renal Failure defined?
Rise in Creatinine of > 26 umol/L within 48 hours
OR
Rise in Creatinine of > (1.5 x levels before injury) within 7 days
OR
Urine output < 0.5 mL/kg/h for > 6 consecutive hours
OR
≥ 25% decline in eGFR within 7 days
What are the stages of Acute Renal Failure?
=> Stage 1
Serum Creatinine > 1.5-1.9 x baseline
Urine output < 0.5 mL/kg/h for 6-12 hours
=> Stage 2
Serum Creatinine > 2.0-2.9 x baseline
Urine output < 0.5 mL/kg/h for > 12 hours
=> Stage 3
Serum Creatinine > 3 x baseline
Urine output < 0.3 mL/kg/h for > 24 hours
What are the risk factors of Acute Renal Failure?
- Age ≥ 65
- Chronic Kidney Disease
- History of AKI
- Use of nephrotoxic drugs in the past week
- Use of iodinated contrast agent in the past week
- Diabetes
- Hypovolemia
How are the causes of Acute Renal Failure categorised?
- Pre renal
- Renal
- Post renal
What are the pre-renal causes of Acute Renal Failure?
Mainly to do with decreased renal perfusion due to:
- Hypovolaemia
- Decreased cardiac output
- Renal artery stenosis
- Systemic vasodilation
What are the renal (intrinsic) causes of Acute Renal Failure?
Relates to the intrinsic damage to the glomeruli, renal tubules or interstitium of the kidneys
=> Glomeulonephritis
- Damage to the glomerulus
=> Acute Tubular necrosis
- Death of tubular epithelial cells
=> Acute Interstitial nephritis
- Inflammation of interstitium
=> Rhabdomyolysis
- Death of muscle fibres which results in their contents being released into the bloodstream - this content causes tubular cell necrosis
=> Tumour lysis syndrome
- Death of cancer cells releasing contents into bloodstream
What are the post renal causes of Acute Renal Failure?
Relates to problems within the renal tract or extrinsic compression
- Renal stones
- BPH
- Pelvic malignancy
What are the clinical features of Acute Renal Failure?
- Dyspnoea
- Orthopnoea
- Paroxysmal Nocturnal Dyspnoea
- Dizziness
- Hypotension
- Arrhythmias
- Pulmonary and peripheral oedema
- Reduced urine output
- Uraemia
What are the features of uraemia?
- Fatigue
- Loss of appetite
- Muscle atrophy
- Nausea and vomiting
=> Pericarditis and encephalopathy
What are the investigations in suspected Acute Renal Failure?
=> Bloods - U&Es, lactate (sepsis marker)
Check levels of Na, K, urea and creatinine
Serum urea : creatinine ratio ≥ 20:1 indicates pre-renal cause of Acute Renal Failure
=> Urine output
< 0.5 mL/kg/h for > 6 consecutive hours indicates Acute Renal Failure
=> Urinanalysis
- Brown casts = Acute Tubular Necrosis
- Presence of leukocytes indicates Acute Interstitial Nephritis as it is an inflammatory process
- Haematuria
=> Ultrasound
- Required in patients presenting with AKI of unknown aetiology
=> Check liver function
What drugs are considered nephrotoxic and should be stopped in cases of Acute Renal Failure?
- NSAIDs
- Aminoglycosides
- ACEi
- Ang II blockers
- Diuretics
What is the management of Acute Renal Failure?
Treatment of the underlying cause and common complication:
- Fluid balance
- Acidosis
- Hyperkalemia
=> Fluid balance - Hypovoleamia:
- Give 500ml of crystalloid (saline) over 15 mins
- Reassess fluid state
- Further boluses of 200-250ml crystalloid
- Stop when euvolemic or by the time 2L are given
=> Fluid balance - Hypervolemia:
- Oxygen supplementation
- Fluid restriction
- Diuretics
- Renal replacement therapy
=> Acidosis
- Treatment of underlying cause
=> Hyperkalemia (if levels ≥ 6.5 mmol/L):
- IV calcium gluconate
- IV combined insulin/dextrose infusion and Nebulised Salbutamol, causing short term shift of K from extracellular to intracellular
- Removal of excess K from body though diuretics, dialysis or calcium resonium
=> Renal replacement is only indicated when the patient is not responding to the medical treatment of complications:
A - Acidosis (pH <7.2)
E - Electrolyte imbalance persistent (K > 7)
I - Intoxication (secondary to toxin)
O - Oedema
U - Uraemia
What drugs are considered safe to take in cases of Acute Renal Failure?
- Paracetamol
- Warfarin
- Statins
- Aspirin
- Clopidogrel
- B blockers
What is Acute Tubular Necrosis?
- Most common renal cause of AKI
- Necrosis of tubular epithelium severely affects function of kidney, as the dead epithelial cells clump together and block the tubules, increasing the pressure within the tubules
What are the causes of Acute Tubular Necrosis?
=> Ischaemic:
- Sepsis
- Shock
=> Nephrotoxins:
- Aminoglycosides
- Rhabdomylosis
- Radiocontrast agents
- Lead
What are the clinical features of Acute Tubular Necrosis?
- Raised urea, creatinine and potassium (although there is more urea in the blood, the levels are not enough to cause the 20:1 ratio)
- Muddy brown casts in urine (dead tubular epithelial cells clumping together and in the tubule)
What are the causes of Acute Interstitial Nephritis - a renal cause of AKI which involves inflammation of the interstitium?
=> Drugs:
- Penicillin
- Rifampicin
- NSAIDs
- Allopurinol
- Furosemide
=> Systemic disease:
- SLE
- Sarcoidosis
- Sjorgren’s syndrome
=> Infection
What are the clinical features of Acute Interstitial Nephritis?
=> Allergic Trad:
- Fever
- Arthralgia
- Rash
- Eosinophilia (white cell casts in urine)
- Renal impairment
- Hypertension
What is the treatment of Acute Interstitial Nephritis?
- Treat underlying cause
- Steroids
What is Rhabdomyolosis?
- Skeletal breakdown in which muscle contents (K, myoglobin) is released into the bloodstream
- The myoglobin is filtered by the glomeruli, causing destruction and inflammation
What are the clinical features of Rhabdomyolosis?
- AKI
- Elevated CK
- Hyperkalaemia
- Myoglobinuria
- Hypocalcaemia (myoglobin binds Ca)
- Elevated phosphate
- Metabolic acidosis
What are the causes of Rhabdomyolosis?
- Seizure
- Collapse/coma
- Ecstacy
- Crush injury
- McArdle’s syndrome
- Statins (especially when co-prescribed with macrolides)
What is the treatment of Rhabdomyolosis?
- IV fluids
- Urine alkilization
What are the features indicating a pre-renal cause of AKI?
- Less flow to kidneys means less blood is filtered
- Urea builds up in the blood, known as azotemia
- Less blood being filtered activates the RAAS system, meaning increased sodium and water reabsorption
- This means serum sodium is increased and urine becomes very concentrated
What are the features indicating a renal cause of AKI?
- Decreased serum urea: creatinine ratio as renal damage means less urea is reabsorbed, more is excreted
- No RAAS system activation therefore increased urinary sodium and decreased urinary osmolality compared to renal causes of AKI
